Sig Sauer P365 Upgrade Part 1

Sig Sauer P365 Upgrade Part 1

Sig fine-tunes the smallest blowback action pistol

By Dennis Adler

In 2019 Sig did what no airgun manufacturer had done before, they designed a Micro Compact blowback action CO2 pistol with a self-contained CO2 BB magazine. That in itself, sold a lot of guns, but in order to make a CO2 pistol this small, one that could use a 12 gram CO2 cartridge, meant that there were some big hurdles for the Sig Sauer’s Sig Air Division engineers to clear. Back in the summer of 2019, Sig Air’s Product Manager Dani Navickas, said that “Sig likes to challenge their R&D engineers, so it was actually a challenge to the R&D team to completely replicate the [9mm] P365 in 1:1 scale so it would be a great training tool. It had to be an equal.” In all of those respects the CO2 model achieved its goals, as I proved in my comparison between the CO2 model and the 9mm pistol last year, but the air pistol nevertheless fell a little short of (consumer) expectations in velocity, and its small size had some unforeseen complications. The first series of P365 models were nevertheless impressive for their authenticity to the 9mm Sig and accuracy with .177 caliber BBs out to 21 feet. For such a small air pistol the precision handling all but made up for the gun’s minor shortcomings.

Mirror, mirror, they’re both Sig Sauer P365 CO2 models, but the one on the right is the upgraded 2020 version, virtually indistinguishable from last year’s P365 blowback action CO2 pistol, until you shoot it! The few minor issues with the original design have been corrected and the action and trigger fine tuned.
Nothing has changed with the packaging or any of the information on handling, shooting, or performance, which is still rated at 295 fps. The P365 still isn’t going to break 300 fps, but I can tell you, with the trigger and action improvements, and the accuracy of the gun, you’re not going to care.
The P365 CO2 model has the exact same lines as the 9mm including the front slide serrations. Even the contours of the barrel in the slide ejection port are the same, which you don’t find even in some more expensive blowback action CO2 models. Also note how trim and well-shaped the thumb safeties and slide release are to the side of the frame, yet they are very easy to work. The entire gun is angled and tapered to minimize mass and aid in easy re-holstering, just like its 9mm counterpart.

Fine tuning

Build a Custom Airgun

Engineers and designers, especially in the world of firearms, being people who strive to do new things or to improve existing things, are never ones to leave well enough alone, and in Sig Air’s R&D department, where feedback from reviewers (journalists) and consumers was taken seriously, the P365 was generating questions about its performance and handling, that Navickas and her team were dedicated to addressing. The P365 models currently in production for 2020 are improved over last year’s guns in small, but meaningful ways.

The 2020 P365 has the same design 12-round CO2 BB magazine but has been fine tuned to provide better performance and reliability. I also found the seating of the CO2 to be a little easier than the previous magazine, though that was not mentioned in my talk with Sig Sauer designers. This is still the smallest 12 gram CO2 BB magazine made.

Not P365 2.0

This isn’t about a new model, let’s say for example, the Umarex Walther PPS and PPS M2, where there are multiple changes to the gun’s (and air pistol’s) design and handling; the changes to the Sig Sauer P365 CO2 model is more about fine tuning the 2020 models to improve performance and handling within the same design.

Changes have been made internally to the magazine and firing system to improve the porting and balance of the valve, making the P365 less temperature sensitive and giving it a “bit more blowback pep” which I will already attest to after doing a short shooting comparison between the two guns. More on this in Part 2. You can also see how all of the white letter warnings have been placed on the underside of the frame and triggerguard to detract as little as possible from the authenticity of design.

One of the things I had pointed out was that due to its small size the CO2 cooled the gun every time you fired it. This lowered pressure and allowed liquid to escape into the ports. The compounding issue was the remarkably small size of the CO2 BB magazine which limited gas chambering and porting, thus making the pistol more sensitive to temperature swings. This, however, had shown no appreciable effect on the gun’s accuracy during my series of tests, but rather on the consistency of function and blowback action. Similar comments arose among consumers and Sig Air engineers addressed this with improvements to the porting and balance of the valve resulting in a P365 air pistol that is now “…less temperature sensitive and with a bit more blowback pep,” according to Sig Sauer.  

The P365 is a masterpiece of air pistol design being a 1:1 training gun for the 9mm version. With dimensions that are within fractions of an inch to the centerfire model, even the contours of the 9mm magazine have been duplicated for the air pistol.

In doing this there was the potential to create a new problem with more force being applied against internal parts, and Sig’s engineers “…decided to tinker with some of the internals on the slide to improve durability and increase the life expectancy of the pistol.” The latter is a big deal, as I’ll explain. Since the P365 CO2 model still cannot be field stripped, these are internal changes you will have to feel, rather than visually inspect. Sig Sauer engineers did, however, have a way to proof their design modifications by subjecting the CO2 model to the same endurance tests, using the same endurance test fixtures as the 9mm model. That means that the latest CO2 pistol design was put through “10,000… 15,000… and even 30,000…cycles and still fired just fine.” I doubt many of us will put 30,000 BBs through the gun.

In a typical blowback action CO2 pistol copying a short-recoil, locked-breech, tilting-barrel design like the centerfire P365, when the slide comes back the barrel tilts up. It does not tilt on the CO2 pistol because the barrel is solidly fixed to the frame (like the barrel on a Walther PPK, not incorrect for traditional blowback action designs, just not what is used on the 9mm P365). You can also see that slide locks back short of its full blowback action movement (0.8125 inches from the back of the beavertail) which approximates the 9mm slide. It locks up shorter (0.437 inches from the back of the beavertail) on an empty magazine due to the barrel and magazine interface. The CO2 model still uses a guide rod and recoil spring and the .177 caliber muzzle is recessed 0.25 inches from the 9mm diameter barrel muzzle for a more authentic look.

Not done yet

The barrel tolerances were improved to increase compatibility with a wider variety of ammo and provide better accuracy across the board. Considering the original test gun was printing 1-inch to 1.5-inch groups at 21 feet with a 3.25 inch barrel, and putting at least five of 10 rounds into groups as small as 0.5 inches, the new model can only go from strength to strength.

Aside from more recoil (which is good in a CO2 blowback action model, not so much in a 9mm centerfire pistol) and a louder report when fired, the most perceptible improvement is the trigger pull. They look the same (the older model is on the left) but when you fire the gun, the difference in feel is significant.

There was one other recurring complaint involving the smoothness of the trigger pull. On the original test gun from 2019’s reviews, trigger pull was a short but firm 5 pounds, six ounces, with 0.3125 inches of total take up to a crisp break. The trigger moved back 0.25 inches with almost zero resistance, and from there was a very firm 0.125 inches to discharge, with no over travel and a quick reset. While heavy in terms of total resistance through the last 0.125 inches of pull, the total trigger pull compared favorably with the centerfire pistol’s 6 pound average, which is also moved back 0.25 inches with almost zero resistance, before a firm pull through of 0.25 inches to break the shot. The trigger on 2020 CO2 models has been improved with some extra polishing here and there to make it feel as close to the 9mm model as possible. We will get into the detail in Part 2, but I can tell you the difference is impressive.

And, of course, with exact 1:1 dimensions, the P365 and its CO2 BB magazine will fit the same gear as the centerfire model. Pictured with the CO2 model are a Galco P365 Stinger Belt Holster and SMC Single Magazine Case.

In Part 2 we will begin comparisons with the 2019 and 2020 models to see how improvements play out.

9 thoughts on “Sig Sauer P365 Upgrade Part 1”

  1. Glad to see that Sig took the feedback seriously and addressed the problems . I had high hopes for the Sig. My ownership of the Mark 1 version lasted about 30 minutes. The first shot and several after that were squib loads. Then after another few shots with the original and spare mag, the velocity again dropped resulting in either bb bounce back or hitting low and failing to even penetrate the target paper, or imbedded in the most superficial layer of the cardboard backing. Returned it with my review that stated “ back to the drawing board”. It seems that is what Sig did. It appears that the valve and cooling ports were to blame. Might take another chance on one.

    • Well worth the chance. Even with the improved magazine alone, my 2019 P365, which was having performance issues similar to yours, only after a couple of months of shooting, was like new again with the magazine that came with the 2020 P365 model. You’ll like the accuracy, too.


  2. Denis – off topic again!
    Re: Barra 1866 Cowboy ‘Pump me Up’ Golden Boy look alike rifle.
    Last week I said I would give a report on MV for the Daisy pellets I was using. Things have changed though and because of its being a pump up gun there are too many variables to look after for that kind of report.
    Instead I decided to just figure it out quickly for best accuracy at 15 yards at 5 pumps.
    What I found was that both Daisy pellet groups opened up considerably from around ½”- .61″ @10 metres to 2½” or greater at 15 metres!
    Not the pellets to use at these not so much longer ranges including the Miesterkugeln 7.0gn.
    All shooting on my indoor range at 68°F or 20°C from an MTD Shooting Rest.
    Going through my collection of pellets shooting 2 or 3 test shots each I found a pellet that seemed to give good repeatable groups. That pellet was the H&N Barracuda Match @ 10.5gn and 4.52mm head size. The 5 shot groups I was testing with (and finally 8 shot groups) were coming in at less than 1 inch at 15 yards.
    Clearly the best pellet for my gun!
    I haven’t given MV a thought while testing and I’m happy with the results
    Still finding it diffilcult to load this rifle so today I ordered a Pellet Pen. Hope it works!

  3. Denis
    Picked up the Pellet Pen At the Post Office this afternoon and hit the indoor range this evening after dinner. Forty shots later I can say the Pellet Pen works way better than I thought it would.
    Not one pellet made its way into the BB magazine which was the major problem I was having and the pellet seater proved invaluable in lineing the pellets up if they were loaded a little off. Also seems to get about twice the number of shots in the same time using the Pellet Pen!
    A recap of my first report on the Barra Cowboy showed little change. Groups opened up a little, probably due to the second cup of coffee after dinner, but were still about 1 inch groups with the 10.5gn H&N Baracuda Match at 15 yards.
    Now I’m looking forward to warmer spring weather and some distance shooting.

Leave a Comment